Background: In 2010, the Clinical and Laboratory Standards Institute (CLSI) revised breakpoints for cephalosporins and carbapenems and indicated that extended-spectrum β-lactamase (ESBL) testing is no longer necessary for Enterobacteriaceae. We compared the results of the CLSI 2010 and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) MIC breakpoints for Enterobacteriaceae producing ESBL and/or plasmid-mediated AmpC β-lactamase (PABL). Methods: A total of 94 well-characterized clinical isolates of Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Salmonella spp., Shigella spp., Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, and Serratia marcescens were analyzed. Of them, 57 were ESBL producers, 24 were PABL producers,and 13 were ESBL plus PABL co-producers. Broth microdilution MIC tests were performed for cefotaxime, ceftazidime, aztreonam, cefepime, and imipenem. Results: Among the 94 isolates containing ESBL and/or PABL, the number of isolates that were susceptible to cefotaxime, ceftazidime, aztreonam, cefepime, and imipenem according to the CLSI 2010 vs. the EUCAST breakpoints were 4 (4.3%) vs. 4 (4.3%); 26 (27.7%) vs. 8 (8.5%); 37 (39.4%) vs. 14 (14.9%); 71 (75.5%) vs. 31 (33.0%); and 76 (80.9%) vs. 90 (95.7%), respectively. Of the 18 isolates that were not susceptible to imipenem according to the CLSI 2010 breakpoints, 13 isolates (72.2%) were P. mirabilis.
Conclusion: The CLSI 2010 MIC breakpoints without tests to detect ESBL and/or PABL for Enterobacteriaceae could be unreliable. Thus, special tests for ESBLs and AmpC β-lactamases are required to detect the resistance mechanisms involved.
배경: 2010년에 Clinical and Laboratory Standards Institute (CLSI)에서는 장내세균(Enterobacteriaceae)에 대한 cephalosporin제와 carbapenem제의 감수성 기준을 변경하면서 이제는 extended-spectrum β-lactamase (ESBL) 검사를 하지 않아도 된다고 하였다. 이에 저자들은 ESBL 및 plasmid-mediated AmpC β-lactamase (PABL)를 생성 장내세균을 대상으로 새로운 CLSI 및 European Committee on Antimicrobial Susceptibility Testing (EUCAST)의 MIC 감수성기준을 적용한 결과를 비교하고자 하였다. 방법: 총 94주의 Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Salmonella spp., Shigella spp., Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, Serratia marcescens를 대상으로 하였고, 57주가 ESBL 생성균주, 24주가 PABL 생성균주, 13주가 ESBL+PABL 동시생성균주였다. 액체배지 미량희석법으로 cefotaxime, ceftazidime, aztreonam, cefepime, imipenem에 대한 MIC를 측정하였다. 결과: 94주의 ESBL 및 PABL 생성균주 중, CLSI 2010 및 EUCAST 기준에 감수성인 균주수는 cefotaxime, ceftazidime, aztreonam, cefepime, imipenem에 대하여 각각 4 (4.3%) 및 4 (4.3%), 26 (27.7%) 및 8 (8.5%), 37 (39.4%) 및 14 (14.9%), 71 (75.5%) 및 31 (33.0%), 76 (80.9%) 및 90주(95.7%)였다. CLSI 2010 기준으로 imipenem 비감수성을 보인 18주 중 13주(72.2%)가 P. mirabilis이었다.
결론: 장내세균에 새로운 CLSI 2010의 MIC 기준을 적용하면서 ESBL 및 PABL 검출을 위한 검사를 하지 않는 것은 유용하지 않을 수 있다. 따라서 ESBL 및 AmpC β-lactamase 등을 검출할 수 있는 검사가 필요할 것으로 생각된다.